Until recently, C. difficile associated diarrhea (CDAD) occurred as an opportunistic infection in older hospitalized patients on antibiotics. Currently, CDAD has become much more worrisome because of widespread increases in its frequency and severity throughout the US and Canada due to the emergence of hypertoxinogenic, binary toxin-producing, quinolone-resistant (Bl) strains. Furthermore, life threatening CDAD is now affecting healthy younger people in communities, even without recent antibiotic use. Even worse, current treatment consisting of more antibiotics is failing and often prolongs shedding or relapses. Hence we urgently need novel approaches that block toxin-induced colitis to prevent the progression of colitis produced by C. difficile toxin(s)) without further disruption of protective flora. This application from the University of Virginia brings together our experienced enterics laboratory team with basic science colleagues in toxin pathogenesis and in drug development, and a pharmaceutical partner (Adenosine Therapeutics, LLC). We shall address the emerging quinolone-resistant C. difficile colitis with an innovative antitoxic approach that is supported by pilot data demonstrating considerable promise. We propose to investigate three types of anti-inflammatory agents alone and in combination: adenosine A2A receptor agonists that block leukocyte activation;A2B antagonists that block cytokine production by epithelial and mast cells, and the pro-absorptive injury repairing agent, alanyl-glutamine. The first three closely interrelated specific aims are designed to determine how these novel therapeutics regulate intestinal cell targets to block toxin-induced apoptosis, inflammation, and secretion. We plan to: 1) use new human intestinal epithelial cell organoid and C57BL/6 murine models to define the targets of purified toxins A and B as well as B-variant and new Bl strain supernatants;2) use C57BL/6 mice with adenosine receptor knockouts and Cre/loxp targeted cellular AaA receptor deletions to define the relevant adenosine targets to inhibition of toxin effects;and 3) use the information gained in aims 1 and 2 to test combinations of A2A agonists, A2B antagonists and alanyl-glutamine, alone and in combination, in animal models in order to prepare for clinical trials of these novel drug therapies for increasingly serious CDAD in humans. Our fourth aim involves discovery efforts towards developing more highly absorbed AaR agonists and the synthesis of the proposed A2A, agonists and A2B antagonists necessary to support this grant.